GANs employ two "dueling" neural networks to train a model to learn the nature of a dataset well enough to generate convincing fakes. When you apply GANs to images, this provides a way to generate often highly realistic still fakes you could use for extremely hard to detect social engineering attacks, especially combined with deep fake videos.

Couldn't get a single one right through intuition alone. Time to start reading I guess...

Edit: after reading the guide, I was able to pick the real faces with around 80% accuracy. However, the site also says current quirks may be "patched" in future algorithms, making it very hard to tell a real picture from a computer-generated one.